Low-Tech Communications Post-IHTF/Invisible Ink!

iinkLow-Tech Communications Post-IHTF/Invisible Ink!

by servantheart, Editor at Large


Have you ever stopped to ask yourself how you would communicate when IHTF? I mean, it’s not like you will be using internet, or any electronics devices, in all likelihood. Even if you still have them at your disposal, you may not want to use them. Since every phone conversation and every email message, fb, pinterest, etc. are all being monitored in real time NOW, just imagine what it will be like post-IHTF.

So, just how would you communicate in such a way as not to give away important information (OpSec)? I honestly do not know; I am hoping to ignite  useful discussion on the subject here.

There is no doubt in my mind we may find ourselves “going back to the future”; returning to low-tech methods of getting many things done, including, perhaps, communications.

One of the thoughts  I had, of course, is carrier pigeons. An Uncle of mine once kept, bred, and trained pigeons. My Aunt hated them. They stank; they were noisy; they were very time-consuming. They need to eat and they need fresh water, every day. They need cages cleaned out regularly, even though the guano, or poop, or whatever you call it for pigeons, fell through the bottom of the mesh cages. Then you had the reproductive issues – managing your flock so you didn’t end up with more pigeons than you could handle.  On the other hand, I’m told pigeons are quite tasty, and were a common food source during WWII. So, one might argue that one could kill the proverbial two birds with one stone: food source and communications!

Naturally, one would need to learn how to train carriers to use them. I’m guessing that takes a lot of time and hard work. So, we may need less time critical methods.

And what if the messages were “captured”, as so often has happened in the past? So then my mind wandered to invisible inks, a.k.a., sympathetic inks. But, how do you make them? I found the answers in a book titled, “Modern Chemical Magic” by Lippy & Palder; these guys are magicians!

A sympathetic (invisible) ink is one that becomes visible when you apply another type of chemical, or handle it in a certain way. They can either be permanently visible, or only temporarily visible (they will vanish again).

Most such inks look like clear water, and, when dry, become invisible on most soft, white papers. 

These guys segregate the secrets by color, so, I’ll just follow their lead.

Today, let’s talk about how to write invisibly with the color, Red. There are a number of ways to do this. Please note that I do not include any warnings or information on these chemicals. Do your homework before messing with any chemical, take prudent precautions, and know what you are doing before you do it (as with anything!).


 (1) 15 grains potassium iodide dissolved in one ounce of distilled water. Sponge over with a solution of 20 grains mercury bichloride dissolved in one ounce water.   

Potassium iodide is the potassium salt form of iodide, a naturally occurring substance. Potassium iodide can be used as an expectorant to thin mucus and loosen congestion in your chest and throat. Potassium iodide is used in people with chronic breathing problems that can be complicated by thick mucus in the respiratory tract, such as asthma, chronic bronchitis, or emphysema.  There are medical warnings that appear to be for too much of it. See:  http://www.drugs.com/mtm/potassium-iodide.html

(2) Weak solution of copper nitrate; when writing is exposed to mild heat, it becomes visible.

Copper(II) nitrate, Cu(NO3)2, is an inorganic compound that forms a blue crystalline solid. Anhydrous copper nitrate forms deep blue-green crystals and sublimes in a vacuum at 150-200 °C

From:  https://en.wikipedia.org/wiki/Copper%28II%29_nitrate

A picture of copper nitrate:


 Isn’t it pretty?!!!

 (3) Use a strong alcoholic solution of phenolphthalein, which becomes invisible when dry. To see it, expose to fumes of a strong solution of ammonia. As ammonia fumes evaporate, writing disappears again. If you want to make it “disappear” immediately, breathe on it.

Phenolphthalein is a mild acid that can be used for medical and scientific purposes. When used in medicine, this compound is most commonly recognized as an ingredient in over-the-counter laxatives. In laboratory settings, it is typically used to test the acidity of other substances.

Phenolphthalein is a crystal powder that is usually white but may sometimes have a yellow tinge. It does not typically have a smell or a taste. It may, however, cause coughing or sneezing if it is inhaled.

From:  http://www.wisegeek.com/what-is-phenolphthalein.htm

(4) A weak solution of silver nitrate, when exposed to heat (after drying) crates a rose-red color.

Silver nitrate is used as the starting point for the synthesis of many other silver compounds, as an antiseptic, and as a yellow stain for glass in stained glass. Most preppers are familiar with silver nitrate, as it is a water purifier. It’s not hard to find.

(5) Use 10% solution of potassium ferrocyanide (sounds serious, doesn’t it?!). Apply a 50% solution of iron tincture to produce a red color.

potassium ferrocyanide:  noun Chemistry .

a lemon-yellow, crystalline, water-soluble solid, K 4  Fe(CN) 6  ⋅3H 2  O, used chiefly in casehardening alloys having an iron base and in dyeing wool and silk.

Also called yellow prussiate of potash.

From:  http://dictionary.reference.com/browse/potassium_ferrocyanide

Sodium ferrocyanide is the main anti caking agent in salt. Further, it is used in the production of Citric acid and pigments, like Prussian Blue.

From:  http://www.gentrochema.nl/index.php/sodium-ferrocyanide/?gclid=CKPdkfPjgLkCFZSY4AodEVQAag

(6) Write with an aqueous solution of iron chloride and allow to dry. Then use a solution of sodium sulfocyanide, and the writing will appear, in red. Well, it was a lot more difficult to find a straight description of sodium sulfocyanide, although suppliers are plentiful, especially in bulk; you’ll have to look this one up for yourself.

Still to come:  more colors and more tips and tricks for invisible writing..stay tuned!

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